The invention relates to a plant for the production of castings in a casting mould stepwise advanced through a pouring and cooling path or guideway and consisting of identical, flaskless mould parts which at each joint of the vertically divided mould provide a casting gravity comprising a chute or inlet which is open at the top side of the mould and during the stepwise advance thereof gets into and out of communication with a bottom outlet of a pouring tundish located above the mould.
Such a plant is for instance disclosed in U.S. Pat. No. 3,996,996 according to which the pouring tundish is held stationary on the stepwise advanced casting mould so that the filling of the pouring cavities is performed automatically, as their inlets coincide successively and one at a time with the bottom outlet of the pouring tundish. To ensure such a coincidence the pouring tundish may, however, be adjustable in the longitudinal direction of the pouring track or guideway and possibly also in the transverse direction thereof.
When pouring an ordinary (grey) cast iron the said pouring tundish is frequently applicable with a fully satisfactory result, but in some cases it may require extra care to avoid slag inclusions in the castings.
The pouring tundish is also applicable in the production of castings of alloyed, seeded and/or nodularised cast iron, that actually requires one or more additives to be added to the molten iron, but then an extra chamber should be provided within the proper casting mould, said chamber being in connection with the pouring cavity inlet and allowing the molten iron and additive to merge or at least to start merging. Otherwise, i.e. if the additive is added in the ladle from which the pouring tundish is being filled, an optimum output of the additive cannot be reckoned on, firstly because the additive gets time to oxidize or evaporate before the moment of the proper pouring, secondly because varying periods of time between the addition and the pouring process may give rise to uncontrollable quality losses as to the castings.
In the production of nodularised castings the use of a particular reaction or processing chamber within the proper casting mould is for instance disclosed in GB-patent No. 1,278,265, and in an article "Inmold Nodulization with Delayed Pouring In Vertically Parted Moulds" by R. Sillen (modern casting/July 1979, page 58-59), a modification of said method is disclosed for use in connection with casting moulds of the above mentioned, special type. According to this modification there is, as far as each pouring cavity is concerned, at the top of the casting mould provided a basin, the volume of which equals the volume of metal needed to fill the casting or pouring cavity and from the bottom of which the inlet extends. The basin is being filled from a processing or reaction chamber, in which the needed amount of additive is at first fed following which the molten iron is being poured. At this time the bottom outlet of the basin is closed by a melting disc and the poured iron with additive from the reaction chamber is thereby temporarily retained in the basin, viz. until the disc has melted. During this " stay period" impurities and slag products can rise to the surface, thereby preventing them from following the cast metal down into the mould cavity during the proper pouring that is effected after the disc has melted and, moreover, the flow of the metal from the open basis may be quiet and without interruption so as to avoid air bubbles in the castings.
According to the article referred to the plant is capable of producing 360 moulds per hour corresponding to a cycle time of 10 sec. This, however, makes heavy demands on the necessary aids for feeding the melting discs, for supplying the additive to the reaction chamber and for pouring the molten iron and, therefore, great investments of the plant must be counted on. It is further considered a disadvantage that the reaction chamber and the basin occupy a certain capacity of the casting mould, thereby restricting the size or number of pouring cavities at each of its joints. It should also be mentioned that a certain volume of metal is retained in the reaction chamber and so represents a loss similar to that caused by the runner and ingate system.